Alpha-olefin isomerization



United States Patent 3,509,228 a-OLEFIN ISOMERIZATION Raymond A. Franz, Kirkwood, and James C. Hill, St.

Louis, Mo., assignors to Monsanto Company, a corporation of Delaware No Drawing. Filed Dec. 31, 1963, Ser. No. 334,918 Int. Cl. C07c /30 U.S. Cl. 260-6832 14 Claims ABSTRACT OF THE DISCLOSURE This process isomerizes internally was saturated monoolefin hydrocarbons to terminally unsaturated monoolefin hydrocarbons using an alkyl aluminum compound and a liquid n-paraffin.

The present invention relates to a process for the conversion of hydrocarbons. More particularly, the present invention relates to a process for the isomerization of internally unsaturated mono-olefin hydrocarbons to terminally unsaturated mono-olefin hydrocarbons.

Recently, it has been found that straight-chain internally unsaturated mono-olefin hydrocarbons may be isomerized to the corresponding straight-chain terminally unsaturated mono-olefin hydrocarbons by reacting internally unsaturated mono-olefin hydrocarbons with dialkyl aluminum hydrides to form n-tri-alkyl aluminum which is then pyrolyzed to yield terminally unsaturated straightchain mono-olefin hydrocarbons. This isomerization method comprises dispersing a dialkyl aluminum in straight-chain mono-olefin hydrocarbons and subjecting the mixture to temperatures of above 150 C. to form n-tri-alkyl aluminum. The n-tri-alkyl aluminum on pyrolysis yields terminally unsaturated mono-olefin hydrocarbons. In this isomerization process, the internally unsaturated mono-olefins are used in a quantity such as to serve both as a reactant and as a solvent for the reaction. Though this process provides a new and useful method for the isomerization of internally unsaturated mono-olefin hydrocarbons to terminally unsaturated mono-olefin hydrocarbons, the yields of terminally unsaturated rnono-olefin hydrocarbons have been somewhat unsatisfactory under this process. The low yields have been found to result from competing reactions, particularly dimerization, and probably, incomplete recovery of the product from the reaction mass.

It is an object of the present invention to provide a new and improved process for the conversion of hydrocarbons. Another object of the present invention is to provide a new and improved process for the isomerization of internally unsaturated mono-olefin hydrocarbons to terminally unsaturated mono-olefin hydrocarbons. Additional objects will become apparent from the following description of the invention herein disclosed.

The present invention, which fulfills these and other objects, comprises intimately co-mixing a reactive alkyl aluminum selected from the group consisting of tri-alkyl aluminum and alkyl aluminum hydride withinternally unsaturated mono-olefin hydrocarbons in the presence of a saturated hydrocarbon solvent at elevated temperatures until alkylation with said internally unsaturated monoolefin hydrocarbons is complete and then subjecting the resulting tri-alkyl aluminum while in the presence of a saturated hydrocarbon solvent to conditions such as to decompose the tri-alkyl aluminum to the corresponding di-alkyl aluminum hydride and recovering terminally unsaturated mono-olefin hydrocarbons as a decomposition product.

The present invention provides three very significant improvements over the prior art. First, dirnerization of "ice the mono-olefin is substantially reduced and, second, the yield of terminally unsaturated mono-olefin hydrocarbons is substantially increased. A third advantage is found in the fact that the present invention has utility for the isomerization of branched-chain internally unsaturated mono-olefin hydrocarbons as well as straight-chain internally unsaturated mono-olefin hydrocarbons to terminally unsaturated mono-olefin hydrocarbons.

The first step of the present invention, herein referred to as the alkylation step, comprises intimately mixing an alkyl aluminum and an internally unsaturated mono-olefin hydrocarbon feed in a solvent which comprises a saturated hydrocarbon. The conditions of this first step are such that the alkyl aluminum is alkylated to a tri-alkyl aluminum having the same number of carbon atoms per alkyl substituent as are in the internally unsaturated mono-olefin hydrocarbons in the feed. It is presently believed that it is at this point that isomerization occurs, either at or during the time the internally unsaturated mono-olefin hydrocarbon is alkylated onto the alkyl aluminum. However, the present invention is not to be limited to any particular theory as to how or when isomerization takes place, but only to the mechanics for carrying out the isomerization.

After alkylation is complete, the second step, herein referred to as the decomposition step, is initiated. Decomposition comprises subjecting the solution of tri-alkyl aluminum in the saturated hydrocarbon solvent to conditions such as to decompose the tri-alkyl aluminum back to the corresponding di-alkyl aluminum hydride and recovering the alkyl group thereby liberated from the trialkyl aluminum, the alkyl group providing the terminally unsaturated product of the present invention.

Both alkylation and decomposition are carried out in the presence of the saturated hydrocarbon solvents described herein with, generally, the same solvent being used in both steps. However, the present invention is not to be so strictly limited since it is within the scope of the present invention that different saturated hydrocarbon solvents be used in each of the two steps of the present invention.

In order to further describe and to illustrate the present invention, the following examples are presented. These examples are not to be construed as limiting the present invention in any manner.

EXAMPLE I Approximately 23.4 grams of a tri-isobutyl aluminum is dispersed with continuous agitation in a solution of 67.5 grams of n-hexene-2 in grams of n-tetradecane. A reaction temperature of l60l65 C. and a reaction pressure of p.s.i.g. is used. There is a continuous evolution of isobutenes from the reaction mass. After approximately 10 hours, alkylation is essentially complete. The pressure is then reduced to atmospheric pressure and the unreacted hexenes distilled from the reaction mass.

To decompose the tri-n-hexyl aluminum, approximately 11 grams of this material were dispersed in 33 grams of n-tetradecane. While nitrogen was passed through the reaction mass as a stripping agent, the temperature was raised to C. and maintained at that temperature until evolution of product Was essentially complete. Substantially atmospheric pressure was used. The mono-olefin product was recovered and found to contain 15% by weight of n-hexene-l. The conversion was approximately 67%. The amount of dimerization which occurred was approximately 3% by weight.

EXAMPLE II The procedure of Example I is substantially repeated in the alkylation step with the exception that no saturated hydrocarbon solvent is used.

The decomposition reaction was not carried out in a saturated hydrocarbon solvent but was carried out at substantially atmospheric pressure under nitrogen and at a temperature of 180 C. In this example, the internally unsaturated mono-olefin hydrocarbons served as both the reactants and the solvents for the reactions. The yield of terminally unsaturated mono-olefin was approximately by weight and the conversion was approximately 61.5%. Approximately 11% by weight of dimer was obtained.

Comparison of the results of Examples I and II is believed to clearly demonstrate the improved and unexpected results obtainable by the use of the present invention. By the process of the present invention, yields and conversion are increased. Further, the amount of dimerization is substantially reduced.

The saturated hydrocarbon solvents in which the alkylation and decomposition steps of the present invention are carried out include cycloparafiin hydrocarbons and branched-chain parafiin hydrocarbons as well as straight-chain paraffin hydrocarbons. The n-parafiin hydrocarbons are preferred hydrocarbon solvents. Among these preferred hydrocarbons are the following non-limiting examples: n-hexane, n-heptane, n-octane, n-nonane', n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane, n-heptadecane, and the like. Generally, the hydrocarbon solvent will be comprised of hydrocarbons of less than 40 carbon atoms per molecule. Preferably, the hydrocarbons of the hydrocarbon solvent will contain no greater than carbon atoms per molecule. The saturated hydrocarbon solvent selected as a solvent should be one which under the conditions of the alkylation step of the present invention will remain in the liquid state. Also, the saturated hydrocarbon solvent is preferably one which has a boiling point no lower than that of the internally unsaturated mono-olefin hydrocarbons in the feed or the terminally unsaturated mono-olefin hydrocarbons formed in the isomerization reaction.

The amount of the solvent used in the present invention is expressed in a molar ratio of solvent to the alkyl aluminum/Usually, this mole ratio is within the range of 0.1 to 50 moles of solvent per mole of the alkyl aluminum. A preferred mole ratio of solvent to the alkyl aluminum is within the range of 1 to moles of the solvent per mole of the alkyl aluminum.

The alkyl aluminum which is alkylated in accordance with the present invention to bring about isomerization of internally unsaturated mono-olefin hydrocarbons may be a reactive tri-alkyl aluminum or an alkyl aluminum hydride. Reactive, as used herein, refers to the ability of the tri-alkyl aluminum or alkyl aluminum hydride to react with the internally unsaturated mono-olefin hydrocarbons to form alkyl aluminum of which at least two or more of the alkyl substituents are derived from the internally unsaturated mono-olefin hydrocarbons in the feed. If the alkyl aluminum is a tri-alkyl aluminum, the alkyl substituents must be displaceable and replaceable by alkylation with the internally unsaturated mono-olefin hydrocarbon feeds of the present invention under the alkylation conditions herein disclosed. Such tri-alkyl aluminum usually is one whose alkyl substituents are relatively loosely held and which may be readily displaced by the mono-olefin feeds of the present invention. Generally, trialkyl aluminums with branching at the beta carbon atom (second carbon atom from the aluminum) are the preferred tri-alkyl aluminurns. Exemplary of such a tri-alkyl aluminum is tri-isobutyl aluminum. I

The alkyl aluminum hydrides useful in the present invention are those which under the alkylation conditions described herein will completely alkylate with the internally unsaturated mono-olefin hydrocarbon feeds of the present invention. Because of the instability of alkyl aluminum di-hydrides, the alkyl aluminum hydride of the present invention is, most often, a di-alkyl aluminum hydride. The preferred di-alkyl aluminum hydride is one having the same number of carbon atoms per alkyl substituent as are in the internally unsaturated mono-olefin hydrocarbons of the feed. In most instances, the di-alkyl aluminum hydride is obtained by decomposing tri-alkyl aluminum. Once the present invention has undergone one complete cycle including alkylation and decomposition, a di-alkyl aluminum hydride is formed and is the aluminum alkyl used in succeeding cycles regardless of What the initial alkyl aluminum may be. The di-alkyl aluminum resulting from decomposition of the tri-alkyl aluminum to produce the terminally unsaturated mono-olefin hydrocarbons in accordance with the present invention has alkyl substituents having the same number of carbon atoms per substituent as are in the mono-olefins in the feed.

Internally unsaturated mono-olefin hydrocarbons of practically any molecular weight may be isomerized in accordance with the present invention. The internally unsaturated mono-olefin hydrocarbons may have the internal unsaturation at any point in the mono-olefin molecule. For example, both hexene-2 and hexene-3 may be isomerized to hexene-l by the present invention. Further, the present process is applicable to either straightor branched-chain internally unsaturated mono-olefin hydrocarbons. For example, 4-methylpentene-2 and 2-methylpentene-Z may be isomerized to the corresponding terminally unsaturated mono-olefin hydrocarbons by the process of the present invention. The present invention finds its preferred utility in the isomerization of internally unsaturated mono-olefin hydrocarbons of 5 to 20 carbon atoms per molecule.

Generally, in practicing the present invention, the amount of internally unsaturated mono-olefin hydrocarbons used is in an amount ranging from one to 15 moles of internally unsaturated mono-olefin hydrocarbon per mole of alkyl aluminum. If it is necessary to both displace and completely replace the alkyl substituents of a trialkyl aluminum or a di-alkyl aluminum hydride, then the amount of internally unsaturated mono-olefin hydrocarbon must be adjusted to take into account the necessity of three moles of mono-olefin per mole of alkyl aluminum. However, after the initial cycle of the present process, the alkyl aluminum is generally a di-alkyl aluminum hydride having the same number of carbon atoms per alkyl substituent as are found in the internally unsaturated mono-olefins of the feed. Thus, for the second and all succeeding cycles, only one mole of internally unsaturated mono-olefin hydrocarbon is used per mole of di-alkyl aluminum hydride. However, in view of the inability to attain efficiency in reaction, it is usually preferred to use an excess of the internally unsaturated mono-olefin hydrocarbon feed. Preferably, the amount of internally unsaturated mono-olefin hydrocarbon used ranges from that amount which is the stoichiometric equivalent of the aluminum alkyls up to 5 times that amount.

The temperatures at which the alkylation step of the present invention is operated will vary to some extent with the molecular weight of the internally unsaturated monoolefin reactants. Higher temperatures are usually preferred as the molecular weight of the reactants increase. However, the alkylation temperatures seldom as below 100 C. or exceed 400 C. At lower temperatures, the reactivity between the di-alkyl aluminum hydride and the internally unsaturated mono-olefin hydrocarbon falls below practical standards. At temperatures higher than the above-defined range, decomposition in the system becomes excessive. In the preferred practice of the present invention, the alkylation temperature is most often within the range of from approximately to 300 C., preferably 150 C. to 250 C.

Alkylation of the di-alkyl aluminum hydride is accordance with the present invention generally is accomplished at a pressure sufficient to maintain the reactants and the solvent in the liquid state. Such pressures are usually within the range of from approximately atmospheric pressure up to 400 p.s.i.g. and higher. Preferably,

pressures of from atmospheric pressure to 300 p.s.i.-g. are used in the alkylation step of the present invention.

The length of time necessary for completion of the alkylation step of the present invention will vary depending upon the alkylation conditions and upon the efliciency of the contact between the internally unsaturated monoolefin hydrocarbons and the di-alkyl aluminum hydride. Generally, the time necessary for alkylation will not exceed 24 hours.

Decomposition of the tri-alkyl aluminum hydride to recover the terminally unsaturated mono-olefin hydrocarbons is carried out under conditions whereby the monoolefin products may be dealkylated from the tri-alkyl aluminum without decomposition of the tri-alkyl aluminum further than to a di-alkyl aluminum hydride. Generally, such conditions include the use of stripping agents such' as inert gases or light hydrocarbons or, preferably, the use of reduced pressures or a combination of these. In the preferred practice of the present invention, decomposition in accordance with the present invention is carried out at a pressure of 0.1 to 760 mm. Hg and/or while an inert stripping agent, preferably a light hydrocarbon or inert gas such as nitrogen, is being passed through the reaction medium. When reduced pressures are used, the preferred pressures are within the range of from to 100 mm. Hg. If an inert stripping agent is used, it is preferred that it be an inert gas or a non-reactive paraifinic hydrocarbon of a lower boiling point than that of the terminally unsaturated mono-olefin hydrocarbons being recovered. When an inert stripping gas is used, it is preferred that it be nitrogen.

The temperatures at which decomposition of the trialkyl aluminum is effected may vary considerably, though will usually not be less than 100 C. or greater than 400 C. Perferably, the decomposition temperatures of the present invention Will be Within the range of from 150 to 300 C.

The method of recovering the terminally unsaturated mono-olefin hydrocarbons produced by decomposition of the tri-alkyl aluminum formed during alkylation may be any conventional means. Usually, the terminally unsaturated mono-olefin hydrocarbon product is recovered by passing the overhead decomposition product through a condensing medium to condense the terminally unsaturated mono-olefin product as it passes from the reaction system during decomposition. The present invention, however, is not to be limited to any particular manner of recovering the terminally unsaturated mono-olefin hydrocarbons produced by the process of the present invention.

The equipment necessary for carrying out the present invention is not critical. It is only required that the equipment as Well as its arrangement follow good engineering principles.

What is claimed is:

1. A process for the isomerization of internally unsaturated mono-olefin hydrocarbons which comprises intimately comixing a reactive alkyl aluminum selected from the group consisting of tri-alkyl aluminum and alkyl aluminum hydride with an internally unsaturated mono-olefin hydrocarbon and a n-parafiin hydrocarbon solvent of no greater than carbon atoms per molecule and having a boiling point no lower than that of the terminally unsaturated monoolefin hydrocarbons formed by such isomerization process, at elevated temperatures until alkylation with said internally unsaturated mono-olefin hydrocarbon is complete, said n-paraflin hydrocarbon solvent being in the liquid phase during said alkylation, thereafter subjecting the resulting tri-alkyl aluminum while dispersed in said n-parafiin hydrocarbon solvent to conditions such as to decompose the tri-alkyl aluminum to the corresponding dialkyl aluminum hydride, said nparafiin hydrocarbon solvent remaining liquid during such decomposition step, and recovering terminally unsaturated mono'olefin hydrocarbons as a decomposition product, said terminally unsaturated mono-olefin hydrocarbons being of the same molecular weight as the internally unsaturated mono-olefin hydrocarbon feed.

2. The process of claim 1 wherein the internally unsaturated mono-olefin hydrocarbon is straight chain.

3. The process of claim 1 wherein the alkyl aluminum is a tri-alkyl aluminum.

4. The process of claim 3 wherein the tri-alkyl aluminum is a tri-alkyl aluminum in which there is branching on the beta carbon atoms.

5. The process of claim 4 wherein the tri-alkyl aluminum is tri-isobutyl aluminum.

6. The process of claim 1 wherein the alkyl aluminum is reacted with the internally unsaturated mono-olefin hydrocarbon at a temperature of to 400 C.

7. The process of claim 1 wherein the pressure at which the alkyl aluminum is intimately co-mixed with the internally unsaturated mono-olefin hydrocarbon is within the range of from atmospheric pressure to 400 p.s.i.g.

8. The process of claim 1 wherein the alkyl aluminum is a di-alkyl aluminum hydride.

9. The process of claim 8 wherein the di-alkyl aluminum hydride is one which has the same number of carbon atoms per alkyl substituent as are present in the internally unsaturated mono-olefin hydrocarbon in the feed.

10. The process of claim 1 wherein the internally unsaturated mono-olefin hydrocarbon is branched chain.

11. The process of claim 1 wherein the tri-alkyl aluminum is decomposed at a temperature of 100 to 400 C.

12. The process of claim 1 wherein the tri alkyl aluminum is decomposed at a reduced pressure of 0.1 to 760 mm. Hg.

13. The process of claim 1 wherein the tri-alkyl aluminum is decomposed while passing a stripping agent through the reaction mass.

14. The process of claim 13 wherein the stripping agent is nitrogen.

References Cited UNITED STATES PATENTS 2,906,763 9/1959 McKinnis 260-448 3,015,669 1/1962 Ziegler et al. 260-448 3,036,016 5/1962 Gordon et al. 2s2- 441 3,163,681 12/1964 Gordon etal 260683.15 3,173,967 3/1965 Brown 260-683.2 3,282,974 11/1966 Bruno et al. 260683.2 X

FOREIGN PATENTS 245,835 2/1961 Australia.

DELBERT E. GANTZ, Primary Examiner V. O KEEFE, Assistant Examiner 

